The present disclosure relates to a liquid crystal display (LCD) device, and more particularly, to a liquid crystal display device capable of improving motion image quality and a method for driving the same.
A liquid crystal display device includes a liquid crystal panel for displaying images and a driving unit for applying driving signals to the liquid crystal panel. Though not shown, the liquid crystal panel includes two substrates and a liquid crystal layer disposed between the substrates. The two substrates are attached to each other with a predetermined cell gap.
A still image is displayed on the liquid crystal panel using a single frame. A motion image is obtained by displaying a plurality of still images on the liquid crystal panel sequentially. The motion image is formed of a plurality of frames, and the liquid crystal layer is continuously driven according to the volume of data signals corresponding to the frames. The volume of the data signal corresponding to each frame is expressed as the level of a gray scale voltage in the liquid crystal layer, which changes molecular arrangement of a liquid crystal in the liquid crystal layer. Since liquid crystal molecules have dielectric anisotropy, dielectric constants of the liquid crystal molecules change according to long axis directions of the liquid crystal molecules. The gray scale voltage of the liquid crystal layer changes according to the dielectric constant. The change of the gray scale voltage significantly reduces response time of the liquid crystal molecules in the liquid crystal layer.
In other words, when a gray scale voltage of a current frame data signal, which is greater than a gray scale voltage of a previous frame data signal, is applied to the liquid crystal, the gray scale voltage of the current frame data signal does not arrive at a desired gray scale voltage immediately because the gray scale voltage of the current frame data signal is affected by the gray scale voltage of previous frame data signal. After several frames pass, the gray scale voltage of the current frame data signal arrives at the desired gray scale voltage. This phenomenon may cause image-sticking, which means that an image of a second frame is overlapped with that of a first frame on the liquid crystal panel. Recently, researches are carried out to improve the response time of the liquid crystal molecules using overdriving compensation data, which has a value greater than a normal value of data corresponding to a signal setting the gray scale voltage.
FIG. 1 is a view illustrating a related art liquid crystal display device including an overdriving circuit.
Referring to FIG. 1, the related art liquid crystal display device includes: a liquid crystal panel 2 for displaying predetermined images; a data driver 6 and a gate driver 4 for driving the liquid crystal panel 2; and a timing controller 8 for controlling the drivers 4 and 6. The related art liquid crystal display device including the overdriving circuit will now be described briefly.
The related art liquid crystal display device further includes an ODC driving unit 10 for modulating input data supplied from an external system into overdriving compensation data to be supplied to the data driver 6.
The over driving circuit (ODC) driving unit 10 includes a frame memory 12 and a lookup table 14. The frame memory 12 delays the input data by one frame to output delayed data. Overdriving compensation data is output using the lookup table 14 according to rates corresponding to the input data and the delayed data.
The lookup table 14 is formed by arranging the input data along X-axis; arranging the delayed data along Y-axis; and inputting the overdriving compensation data at an intersection point of X-axis and Y-axis. The input data and the delayed data are input to the lookup table 14, and then the lookup table 14 outputs the overdriving compensation data corresponding to an intersection point of the input data and the delayed data to the data driver 6. The data driver 6 converts the overdriving compensation data into analog voltages to be applied to the liquid crystal panel 2. A gray scale voltage of a liquid crystal disposed in the liquid crystal panel 2 is increased using the overdriving compensation data.
As such, the ODC driving unit 10 outputs the overdriving compensation data to be applied to the liquid crystal panel 2. The ODC driving unit 10 outputs the overdriving compensation data according to the rates corresponding to change of a gray scale. When a fast motion image is displayed on the liquid crystal panel 2, the sharpness of the motion image is deteriorated by slow response time of the liquid crystal panel 2. In here, the ODC driving unit 10 prevents the deterioration of the sharpness. On the contrary, in the case where the ODC driving unit 10 is applied to still images, the sharpness of the still images is deteriorated.
Furthermore, the still images do not need the ODC driving unit 10, the application of the ODC driving unit 10 to the still images increases power consumption unnecessarily.